गॉसियन प्लम मॉडल (Gaussian plume model) में, किसी प्रदूषक की ज़मीनी स्तर पर सांद्रता अधिकतम कब होती है?

Prolonged exposure to extreme cold temperatures may result in tissue damage known as frostbite, which is categorized as a:

In the context of ecosystem energy dynamics, which of the following expressions correctly defines Net Primary Productivity (NPP)?